Automatic transmission control logic may be utilized to match one of a plurality of transmission gear ratios to the operation of the vehicle intended by the driver, such as acceleration or braking, to improve the driving experience. For example, automatic transmission control logic may be used to supplement or assist the brake system of the vehicle with engine braking. Engine braking may be facilitated by reducing the gear ratio of the transmission by downshifting the transmission as the vehicle decelerates. In addition to matching the transmission gear ratio to the intended vehicle operation, transmission control logic may also be used to account for certain road and/or driving conditions such as road grade, vehicle load, weather conditions and the like when the vehicle is accelerating or braking. Current transmission control logic estimates braking efforts based on vehicle deceleration levels to determine downshift aggressiveness which, in turn, is used to modify transmission downshift points. However, when a load is added to the vehicle the deceleration characteristics of the vehicle may change and, as a result, the same brake effort will not produce the same deceleration. Current transmission control logic has a major flaw in that the logic fails to account for applied loads and the change in the deceleration characteristics of the vehicle that result.
Accordingly, a method and system for adjusting the downshift points of a vehicle transmission to assist in vehicle braking is needed which accounts for increased vehicle loads.